1. Field of the Invention
The present invention relates to a signal processing device for identifying a signal and a signal processing method, and more particularly to a signal processing device for identifying an image source and a signal processing method.
2. Description of the Related Art
In the case where an image formed for a movie is broadcasted in television broadcasting, it is necessary to convert a picture recorded on a film (film source) of the movie into an NTSC signal. In general, while a film source of a movie or the like has 24 frames per second, an NTSC television system has 30 frames per second (60 fields per second), and the conversion is needed from this. As a conversion method, there is a frame number converting processing such as “3-2 pull-down (3:2 pull-down)” processing for converting a film source of 24 Hz into an NTSC signal of 60 Hz.
Specifically, the 3-2 pull-down processing is such processing that in continuous two frames of the film source, the first frame is read out as three fields of video signals, the next frame is read out as two fields, and such readout operation is repeated. For example, as shown in FIGS. 8A to 8B, three fields A, A′, A are read out as video signals from a first frame of an original film source (Original Film Source 24 Hz-Progressive), and two fields B and B′ are read out as video signals from a next frame of the original film source. In this way, in the 3-2 pull-down processing, continuous fields having the same image content are read out as 3, 2, 3, 2, 3 . . . fields as video signals. This is different from normal NTSC signals having different motion phases among all fields.
Incidentally, as a method of converting a picture recorded on a film source into an NTSC signal, there is also a method of repeating each frame three times, or a method of removing a field every other frame.
There are many devices for subjecting an NTSC signal to a signal processing. For example, a scanning line number doubling device is a signal processing device which can subject the NTSC signal to a scanning line doubling processing. On the other hand, as the NTSC signal, there are a normal NTSC signal and an NTSC signal subjected to the 3-2 pull-down processing as described above. From this, it is important to previously know (detect) whether the signal inputted to the signal processing device is the normal NTSC signal or the signal subjected to the 3-2 pull-down processing, in order to realize an optimum signal processing.
As methods for detecting an NTSC signal (hereinafter referred to as a 3-2 pull-down source) generated from a film source, there is such a method that motion detection is made when the source is inputted and it is classified as the 3-2 pull-down source. Such a method is a complicated one requiring an extremely large logic.
In most of these methods, various kinds of block matching methods are used in which not only an input of a source is detected, but also a motion vector is added to each object of a picture. Besides, although there are various applications, there is only one flag indicating that the input source is the 3-2 pull-down source and the phase of a current field is required.
Besides, in the foregoing methods, there are problems as follows:
In an application in which the motion vector is not used except at the detection of the 3-2 pull-down source and the detection of the phase of a current field in the sequence of the 3-2 pull-down source, a logic gate becomes very expensive in the foregoing block matching.
Besides, in order to detect the motion vector, that is, in order to detect the 3-2 pull-down sequence and the signal of the phase of the current field in the sequence, various kinds of post-processings become necessary.
Besides, the detection speed of a present system depends on the speed of convergence of the motion vector. This is contrary to the reliability of the motion vector.